Photosensitive elements are widely used as resist materials for etching and plating in the field of printed circuit board manufacturing. Photosensitive elements are usually obtained by forming a photosensitive layer composed of a photosensitive resin composition on a support and forming a protective film on the photosensitive layer. Photosensitive elements can be used to form resist patterns in the following manner. First, the protective film of the photosensitive element is released and the photosensitive layer is laminated on a board (copper board). Next a patterned phototool is contact bonded to the support, irradiated (exposed) with active light rays such as ultraviolet rays, and then sprayed with a developing solution to remove the unexposed sections.
With the increasing high densities and high definitions of printed circuit boards in recent years, demand has been growing for photosensitive elements with higher resolution and adhesiveness. Higher sensitivity is also being demanded of photosensitive elements for improved productivity of printed circuit boards. It has been attempted to improve the properties of photosensitive resin compositions in order to meet such demands (see Patent document 1).
On the other hand, there is also increasing interest in resist pattern forming methods based on “direct writing exposure”, which involve direct writing without using phototools. It is generally accepted that direct writing exposure methods allow formation of resist patterns with high productivity and high resolution. Laser direct writing exposure and DLP (Digital Light Processing) exposure methods may be mentioned as typical direct writing exposure methods. In laser direct writing exposure, it has become practical to implement gallium nitride-based blue laser light sources that emit laser light with a wavelength of 405 nm, and that have long life and high output. The use of such short wavelength laser light for direct writing exposure is expected to allow formation of high-density resist patterns that have been difficult to produce in the prior art. DLP exposure, a process employing the DLP system advocated by Texas Instruments, has been proposed by Ball Semiconductor Co., and exposure devices that apply this process have already begun to be implemented.
The photosensitive element described in Patent document 1 is designed for total wavelength exposure by a mercury lamp light source, centered on light with a wavelength of 365 nm. Consequently, the sensitivity of the photosensitive element for exposure light (for example, violet semiconductor lasers centered on light with a wavelength of 405 nm) in direct writing exposure is low, making it difficult to adequately improve productivity. A photosensitive element has also been proposed that contains a hexaarylbiimidazole compound and titanocene compound as radical generators and a dialkylaminobenzene compound as a sensitizing dye (see Patent document 2).
[Patent document 1] Japanese Patent Application Laid-open HEI No. 10-110008
[Patent document 2] Japanese Patent Application Laid-open No. 2002-296764